Canon EOS 1300D - Manual (Page 112)

f : Changing the Depth of Field
112
To obtain a correct flash exposure, the flash output will be set
automatically to match the set aperture (autoflash exposure). The
shutter speed will be set automatically between 1/200 sec. - 30 sec. to
suit the scene’s brightness.
In low light, the main subject is exposed with the auto flash metering,
and the background is exposed with a slow shutter speed set
automatically. Both the subject and background look properly exposed
with a touch of atmosphere (automatic slow-speed flash sync). If you
are handholding the camera, keep it steady to prevent camera shake.
Using a tripod is recommended.
To prevent a slow shutter speed, under [53: Custom Functions
(C.Fn)], set [3: Flash sync. speed in Av mode] to [1: 1/200-1/60sec.
auto] or [2: 1/200sec. (fixed)] (p.261).
The aperture opening (diaphragm) changes only at the moment when
the picture is taken. Otherwise, the aperture remains fully open.
Therefore, when you look at the scene through the viewfinder or on the
LCD monitor, the depth of field will look narrow. With the procedure
below, you can check the depth of field before taking the picture.
1
Enable depth-of-field preview to be used.
 Under [53: Custom Functions (C.Fn)], set [9: Assign SET
button] to [4: Depth-of-field preview] (p.266).
 For details about Custom Function settings, see page 258.
2
Exit the menu.
 Press the <M> button two times to exit the menu.
3
Press the <0> button.
 The aperture will be stopped down so you can see the depth of field.
D Using the Built-in Flash
3 Depth-of-Field PreviewN
While looking at the Live View image (p.140) and holding down the <0>
button, you can change the aperture and see how the depth of field changes.